Thought Exercise,how do you think timetravel changes history

[AniThyng]

The 2nd point you made hammers home the fact that in some model's of time travel, you effectively become a "mass murderer" by preventing the existence of billions of people who would never be born after your time altering stunt. Sure, you killed Hitler and prevented WW2, but then now the entire generation of Isreali's born of the consequences of WW2 will never exist. Ever.

Just like how every time you use contraceptives, you're murdering a child? Do the people caused by the alternate timeline have less of a right to live than the ones from the original?

Every time you make a choice, you prevent the alternatives from happening. It's just that in this case, we know, exactly, what would have been the outcome of the alternative.

At this point, does anyone at all have a right to anything, really? Under these scenarios, in a time-travel model where you literally change the future by changing the past, there could be an infinite amount of changes that happen, and we don't percieve it because it's "always been that way". - most time travel stories work because the viewpoint character somehow manages to not be affected or retains his memory of the "original" timeline. But I'm taking as a premise that there is a starting timeline A that is how things would have happened if there was never any time travel. And from the point of view of a time traveller that remembers timeline A as his timeline, a timeline B where everyone he ever knew would never be born is in its own way a tragedy. It may not be a moral tragedy, but it's still sobering nonetheless. It's not the same as a child that never was due to a condom use in a linear time world with no time travel.

[Simon_Jester]

The other thing you have to be worried about with your time machine is that it has to also be a space-machine, otherwise you'll succesfully jump to the 15th century, but the Earth is in a completely different point in space, so you land in hard vacuum instead.

Eh, teleporting through space is trivial compared to teleporting through time.

The 2nd point you made hammers home the fact that in some model's of time travel, you effectively become a "mass murderer" by preventing the existence of billions of people who would never be born after your time altering stunt. Sure, you killed Hitler and prevented WW2, but then now the entire generation of Isreali's born of the consequences of WW2 will never exist. Ever.

(In the Axis of Time trilogy, the part that stands out to me is when Kolhammer reflects that rather than his son dying in a war, his son will now simply never be (his wife of course, had not yet been born, and with the changed timeline and the vagarities of conception, she may never be) and it's somehow more sad that way.)

I don't think that this definition of murder is viable, because it implies that any situation which makes it impossible for a hypothetical person who does not yet exist to exist in the future is murder.

That's even more extreme than saying contraception is murder. I mean, think about the "vagaries of conception" you mentioned. When you were conceived, billions of other potential people who could have existed suddenly became impossible, because it was you or (one of) them. Does that make you somehow responsible for mass murder?

At this point, does anyone at all have a right to anything, really? Under these scenarios, in a time-travel model where you literally change the future by changing the past, there could be an infinite amount of changes that happen, and we don't percieve it because it's "always been that way". - most time travel stories work because the viewpoint character somehow manages to not be affected or retains his memory of the "original" timeline. But I'm taking as a premise that there is a starting timeline A that is how things would have happened if there was never any time travel.

And from the point of view of a time traveller that remembers timeline A as his timeline, a timeline B where everyone he ever knew would never be born is in its own way a tragedy. It may not be a moral tragedy, but it's still sobering nonetheless. It's not the same as a child that never was due to a condom use in a linear time world with no time travel.

From a psychological standpoint, that's true, I suppose, but it doesn't hold much water philosophically.

Also, that model (timeline B overwrites timeline A) has a huge problem in that it leads to paradoxes. Imagine I go back in time and avert World War Two- but my grandfather married my grandmother a few years after her first husband was killed in the war. I can go visit my (much younger) grandparents... but they're never going to meet. One of my parents are never conceived, which is tragedy, but I am never conceived, which is worse than tragedy- it's paradox.

In order for me to exist and have affected the universe (multiverse)? Timeline A has to still exist "somewhere out there." I, as a time traveller, am an effect that requires a cause, and that cause lies on Timeline A. So I can't overwrite my own past and thus "destroy" the people I knew. All I'm doing is creating a place that they aren't in. It's reasonable for me to miss them, but I haven't "unmade" them in any meaningful sense.

[adam_grif]

Like I said. The only difference in this case is that you happen to know exactly what the outcome would have been had you not made things go differently.

[RedImperator]

Just so you guys know, the non-identity problem (that is, the problem of how people who don't exist--future persons--can be worthy of moral consideration) remains one of the great unsolved conundrums of contemporary ethics. So, if you guys work out a solution to it, be sure to let Peter Singer know.

[RowanE]

I'd go with the law of conservation of history/novikov self-consistency principle, because it seems like the simplest way to avoid paradoxes in a universe - the chance of successfully creating a paradoxical event is simply zero. But i'd expect the only part of the timeline that actually needs to stay the same is that of the timetravellers themselves - as long as they are exactly the same when they arrive in the past, it's not a paradox.

So, as long as the time machine gets invented, and the same timetravellers go back with the same memories, nothing's wrong. So you can change anything else - you could even take over the world in 2000BC, and just fake an entire upbringing for your own future self, when you get born - everyone you know before you enter the time machine could be an actor, Truman Show style, while every bit of the earth you didn't see is an epic dystopia devoted to the worship of the timetravellers and their descendents, who rule all humanity. Or a utopia with just a few statues to these founding fathers. But if you're not able or willing to do that, you'd have to cover up the changes.

I hadn't thought about quantum changes until i read this thread... that's really unsettling, i'd always wanted to travel in time but i don't think i'd want to now. Although, because of what i've said above, it's likely that everyone famous, and eveyone you know personally, would still be born this time around, by chance, because otherwise there might be a paradox - you'd go into the time machine with a different set of memories, etc.
So it'd just be strangers you never heard of that would be completely different people this tme around. Well, if i'm potentially-annihilating a couple billion i don't know about, that's alright